This is a photo of a relatively small-size table fitted with an electro-magnetic coil. Such tables are called magnetic tables or sometimes also juice table. The electro-magnetic coil is used to control magnetic dice.
At first glance the magnetic coil appears to be very simple and perhaps even easy to make. however, there are several issues involved.
First potential issue is noise. If the coil is not made right, it will produce a buzzing noise; same kind of noise that is produced by some high-power transformers. This noise is produced by the pulsating magnetic field moving some of the components of this gaff.
The other issue has to do with the polarity and power. Since the unit needs to produce a high-power magnetic field it also has to get a lot of power to work. If the unit is powered up by an AC (alternating current) power source the current needs top be converted to DC (direct current) at some point because alternating current would produce an equally alternating magnetic field polarity. In other words, if we connect a coil to an AC power source, the coil would end up producing a magnetic field that is constantly alternating from North to South. If dice were to be placed over such magnetic field they would keep moving rapidly while the magnet is powered up. If this unit is to be powered by batteries, however, then there are some other issues. The coil needs a lot of power, so the batteries have to be very strong and quite heavy.
There are some other technical issues, even more complicated, but for the purpose of this explanation it is not necessary to get into all the technical details. What it all boils down to is that good units are not easy to make and therefore also hard to find.
This particular table is actually a multi-functional cheating table, as the magnetic coil is not permanently built-in. The table top comes off so the coil can be removed and replaced by a different gaff, such as an X-RAY unit for reading cards.
Below is a clipping from an old HC Evans Blue Book, crooked gambling catalog, showing a listing for an electro magnet that was sold at that time by the company, very similar in appearance to the magnet shown above.